Armed with a radio antenna and a cassette player, Chris Templeton navigates thick underbrush, scanning the trees at Discovery Park for a tiny brown bird.

Following beeps from a receiver strapped over his shoulder, he stalks toward a large tree and plays back a recorded bird song. A song sparrow responds with sharp whistles, chirps and trills.

"He's singing to defend his territory," Templeton explains. "They learn songs early in life from their neighbors."

Templeton, a biology doctoral student at the University of Washington, is studying the ways birds encode information about their environments and pass it on to other birds.

He's discovered that song sparrows have a much bigger "vocabulary" than once thought. And he's found that chickadees — those little black, white and brown birds that frequent back-yard feeders — use a sophisticated call system that varies their characteristic "chick-a-dee-dee-dee" depending on the threat they face.

Templeton's chickadee study is published in the current issue of the journal Science.

On a recent day at Discovery Park, Templeton, 28, and student assistant Elena Wagner, 20, were trying to catch a group of young sparrows to replace the batteries in radio transmitters fitted on the birds in the spring. Templeton attached the devices to help track the sparrows in thick trees.

The researchers played recorded sparrow songs, waited for the birds to fly toward the song and then drove them into a finely strung net.

The juveniles are more difficult to track because they haven't yet established a territory.

"They seem to have two different home ranges, which can be almost a kilometer apart," Templeton said. "I think they are learning different songs in several different neighborhoods."

Templeton believes that by learning a variety of songs, the birds can fit in with their neighbors and increase their chances of establishing a territory once it's time for them to find a mate.

How birds learn

For the past two years, Templeton has been tracking song sparrows at Discovery Park, in Seattle's Magnolia neighborhood overlooking Puget Sound.

He also is working in the lab with other biology researchers at the UW to understand how young sparrows learn songs. The birds are hard-wired to pick up the songs but actually learn them from adults.

Templeton brings a background in music to his work. He's a saxophonist trained in jazz and classical music and has performed in a number of concert bands and jazz ensembles.

"Music is such an important part of me," he said. "I hear it in my head, my brain is cued into it and my ears are well trained for that sort of thing. When I'm outside listening to birds I hear things other people might not be tuned in to."

His combined interest in song and biology led Templeton to study bird vocalization at the University of Montana, where he got his master's degree in 2002. That's also where he completed his published chickadee research.

The study deciphers the "chickadee-dee" alarm calls of black-capped chickadees, which are common throughout much of North America.

Evidence suggests that depending on the size and threat of a perched predator, such as a pygmy owl, a chickadee calls with a specific number of "dees." The calls attract flock mates to swarm and dive bomb the predator.

"It's like a swarm of mosquitoes; they are trying to frustrate the predator so it leaves the territory," Templeton said.

He and his co-authors recorded chickadee calls for certain predators and then played these back through camouflaged speakers, observing the birds' mobbing behavior.

"If we played them the call that should mean pygmy owl, more birds would mob and swarm in the direction of the speaker," he said. For the north pygmy owl, Templeton and his co-authors recorded up to 21 "dees" in the call.

They also analyzed the calls with a spectrograph, a device that converts sound waves into a spectrogram that can be read like a sheet of music.

The analysis revealed complex variations in the intensity, length and overtone of the "dees." These calls varied for different predators, even those that look similar.

"Never before have we seen an animal that had such a sophisticated call system. They can distinguish predators with such complex information in such subtle calls," Templeton said.

Complex learning

Among birds, calls generally warn of predators, while songs assert territory and attract mates. While the black-capped chickadee has complex calls, it has only one song, a "fee-bee" that sounds like a two-tone whistle. The song sparrows in Templeton's current research learn a number of songs but have very few calls.

"Birds have a really complex brain for this learning, especially given the size," Templeton said. "Their brains are so small yet they have these really well-developed areas in the brain."

Those areas grow when birds are learning songs and finding mates and shrink in the nonbreeding seasons.

Templeton came to the University of Washington to work with Michael Beecher, a professor of biology and psychology who investigates bird vocalization and behavior. Beecher has tracked song sparrows at Discovery Park since 1986.

Tracking sparrows in the wild has been difficult, but improvements in radio-transmitting technology make it easier to monitor the birds and observe how they learn.

And the work keeps Templeton outside, where he prefers to be. He says he's always observing animals, whether he's on the Burke-Gilman trail or in his own back yard.